JQuery Mobile Pinch Zoom Image Only
you can do this on image:
var image=document.getElementById('imageId');
image.addEventListener('gesturechange',function(e){
if(e.scale>1){
//zoom in
//increase the size of image according to the e.scale
}
else if(e.scale<1){
//zoom out
//decrease the size of image according to the e.scale
}
});